Orthopaedic knee implant system with controlled stiffness

ABSTRACT

A tibial implant includes one or more stiffness-modifying features to reduce the stiffness of one or more sections of the tibial implant. The stiffness-modifying features may include slots, recesses, or passageways defined in various locations of the tibial implant to selectively reduce the stiffness of a tibial insert and/or tibial base of the tibial implant.

This application is a continuation application of, and claims priorityto, U.S. patent application Ser. No. 16/863,112, which was filed on Apr.30, 2020, now U.S. Pat. No. 11,439,511, the entirety of which isexpressly incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to orthopaedic systems, and, moreparticularly, to orthopaedic systems for performing knee replacementsurgery.

BACKGROUND

Joint arthroplasty is a well-known surgical procedure by which adiseased and/or damaged natural joint is replaced by a prosthetic joint.A typical knee prosthesis includes a tibial tray, a femoral component,and a polymer insert or bearing positioned between the tibial tray andthe femoral component. Depending on the severity of the damage to thepatient's joint, orthopaedic prostheses of varying mobility may be used.For example, the knee prosthesis may include a “fixed” tibial insert incases wherein it is desirable to limit the movement of the kneeprosthesis, such as when significant soft tissue damage or loss ispresent. Alternatively, the knee prosthesis may include a “mobile”tibial insert in cases wherein a greater degree of freedom of movementis desired. Additionally, the knee prosthesis may be a total kneeprosthesis designed to replace the femoral-tibial interface of bothcondyles of the patient's femur or a uni-compartmental (or uni-condylar)knee prosthesis designed to replace the femoral-tibial interface of asingle condyle of the patient's femur.

The type of orthopedic knee prosthesis used to replace a patient'snatural knee may also depend on whether the patient's posterior cruciateligament is retained or sacrificed (i.e., removed) during surgery. Forexample, if the patient's posterior cruciate ligament is damaged,diseased, and/or otherwise removed during surgery, aposterior-stabilized knee prosthesis may be used to provide additionalsupport and/or control at later degrees of flexion. Alternatively, ifthe posterior cruciate ligament is intact, a cruciate-retaining kneeprosthesis may be used.

One consideration of joint arthroplasty is bone growth around or nearthe implanted knee prosthesis. Bone tissue growth and resorption isdirectly related to the loading experienced by the bone tissue. Thisphenomenon, which is referred to as Wolfe's law, results in abnormalgrowth of bone tissue that experiences abnormal loading. Abnormal growthof the bone tissue may be, for example, a result of stress shieldingwhere the bone density is considerably lower in a region adjacent to animplant. The bone density lowers due to the implant experiencing thebrunt of the load in the region, i.e., the implant shields the bone fromstress, resulting in reduced density. The reduced density can weaken thebone tissue in the region to a point where there is an increased risk offurther dysfunction or damage, such as fracturing.

One particular issue with orthopaedic implants in view of Wolfe's law isthe geometric and material requirements. Orthopaedic implants,generally, comprise materials other than bone tissue, such as variousmetals and/or polymers. The materials may be chosen to match thematerial properties of native bone tissue as closely as possible, but aperfect match is difficult to achieve. Further, the shape of the implantmust match the shape of the portion of bone that is resected to allowimplantation. This is particularly important with regards to thicknessesof the implant in various regions, which may have a thickness thatresults in excessive stiffness in order to properly fill the jointspace. These two issues can contribute to abnormal bone loading.

SUMMARY

The present invention provides an orthopaedic knee system including oneor more components with a modified stiffness to simulate natural loaddistribution on bone tissue and reduce the risk of, for example, bonedensity loss due to stress shielding and other bone tissueabnormalities.

According to an aspect of the present disclosure, a tibial insertincludes a medial articular surface, a lateral articular surface, and acentral body formed between the medial articular surface and the lateralarticular surface, wherein the central body includes astiffness-modifying feature.

In some embodiments, the stiffness-modifying feature may include agroove defined in the central body. Additionally, in some embodiments, atherapeutic agent disposed in the groove. The groove may be linear orcurved when the tibial insert is viewed in a transverse plane. In someembodiments, the groove may extend from an anterior side of the tibialinsert to a posterior side of the tibial insert. For example, the groovemay extend linearly from an anterior side of the tibial insert to aposterior side of the tibial insert. Alternatively, the groove may curvefrom an anterior side of the tibial insert to a posterior side of thetibial insert.

In some embodiments, the tibial insert may further includes a postextending superiorly from the central body. In such embodiments, thestiffness-modifying feature may be embodied as a firststiffness-modifying feature defined in the central body medially of thepost and a second stiffness-modifying feature defined in the centralbody laterally of the post. In some embodiments, each of the first andsecond stiffness-modifying features include is a groove defined in thecentral body. Additionally, in some embodiments, at least one of thegrooves is a linear when the tibial insert is viewed in a transverseplane. Additionally or alternatively, at least one of the grooves may bea curved when the tibial insert is viewed in a transverse plane.

In some embodiments, the central body may include an inner wall thatdefines the stiffness-modifying feature. For example, the inner wall maydefine a groove in the central body, such as a curved or linear groove.Additionally, in some embodiments, stiffness-modifying feature mayinclude a passageway defined in the central body. The passageway may beembodied as a blind passageway having an opening on an anterior side ofthe central body or a posterior side of the central body. Alternatively,the passageway extends through the central body and may include a firstopening on an anterior side of the central body and a second opening ona posterior side of the central body. In some embodiments, the tibialinsert may include a therapeutic agent disposed in the passageway.Additionally, in some embodiments, the tibial insert may include agroove defined on a top surface of the central body, and the groove isin fluid communication with the passageway. The groove may define a pairof tabs of the central body, which may be movable into the passageway inresponse to a force applied to the tabs. A therapeutic agent may bedisposed in the passageway, and the tabs may cause a release of thetherapeutic agent from the passageway in response to the force. Further,in some embodiments, the tibial insert may include a pair of openingsdefined on an anterior side of the central body. In such embodiments,each of the openings may be configured to receive a tensioner operableto move the tabs of the central body to cause the release of thetherapeutic agent form the passageway.

According to another aspect, a tibial prosthesis for implantation into asurgically-prepared tibia of a patient may include a platform and arail. The platform may include a top surface configured to receive atibial insert. The rail may be coupled to a periphery of the platform.The rail may also include a stiffness-modifying feature.

In some embodiments, the stiffness-modifying feature is a slot definedin the rail. For example, the stiffness-modifying feature may beembodied as a rail section having a height, relative to the top surfaceof the platform, that is less than a height of an adjacent rail section.Additionally or alternatively, the stiffness-modifying feature mayinclude a recess defined in the top surface of the platform. In someembodiments, the tibial prosthesis may include a therapeutic agentdisposed in the recess.

Accordingly to yet another aspect, a tibial prosthesis for implantationinto a surgically-prepared tibia of a patient may include a platformhaving a bottom surface and a keel extending inferiorly from the bottomsurface of the platform. The keel may include a stiffness-modifyingfeature. In some embodiments, the stiffness-modifying feature may beembodied as an undercut defined in the keel adjacent to the bottomsurface of the platform.

According to a further aspect, a tibial prosthesis for implantation intoa surgically-prepared tibia of a patient may include a polymer platformand a keel. The polymer platform may have a superior surface and aninferior surface opposite the superior surface, and the keel may extendfrom the inferior surface of the polymer platform. The polymer platformincludes a plurality of stiffness-modifying features defined in theinferior surface. In some embodiments, the one or more of the pluralityof stiffness-modifying features may be embodied as a slot defined in theinferior surface of the polymer platform. For example, the slot(s) maybe defined in the inferior surface of the polymer platform in ananterior-posterior direction. Additionally or alternatively, theinferior surface of the polymer platform may include a porous ingrowthsurface and at least two slots of the plurality of slots may intersecteach other.

BRIEF DESCRIPTION OF THE DRAWINGS

The detailed description particularly refers to the following figures,in which:

FIG. 1A is a superior plan view of a tibial insert includingstress-modifying features defined in a top surface of a body of thetibial insert;

FIG. 1B is a superior plan view of another tibial insert includingstress-modifying features defined in a top surface of a body of thetibial insert;

FIG. 2A is a superior plan view of a tibial insert, similar to thetibial insert of FIG. 1A, and having different stress-modifying featuresdefined in a top surface of a body of the tibial insert;

FIG. 2B is a superior plan view of a tibial insert, similar to thetibial insert of FIG. 1B, and having different stress-modifying featuresdefined in a top surface of a body of the tibial insert;

FIG. 3 is a perspective superior view of another embodiment of a tibialinsert having stress-modifying features defined therein;

FIG. 4A is an anterior perspective view of a tibial base including akeel having stress-modifying features defined in the keel;

FIG. 4B is a bottom perspective view of the tibial base of FIG. 4A;

FIG. 4C is an anterior perspective view of a known tibial base;

FIG. 5 is an inferior perspective view of a polymer tibial base havingstress-modifying features defined on a bottom surface; and

FIG. 6 is an inferior perspective view of another polymer tibial basehaving stress-modifying features defined on a bottom surface.

DETAILED DESCRIPTION OF THE DRAWINGS

While the concepts of the present disclosure are susceptible to variousmodifications and alternative forms, specific exemplary embodimentsthereof have been shown by way of example in the drawings and willherein be described in detail. It should be understood, however, thatthere is no intent to limit the concepts of the present disclosure tothe particular forms disclosed, but on the contrary, the intention is tocover all modifications, equivalents, and alternatives falling withinthe spirit and scope of the invention as defined by the appended claims.

Terms representing anatomical references, such as anterior, posterior,medial, lateral, superior, inferior, etcetera, may be used throughoutthe specification in reference to the orthopaedic implants and surgicalinstruments described herein as well as in reference to the patient'snatural anatomy. Such terms have well-understood meanings in both thestudy of anatomy and the field of orthopaedics. Use of such anatomicalreference terms in the written description and claims is intended to beconsistent with their well-understood meanings unless noted otherwise.

Referring now to the drawings, and more particularly to FIGS. 1A and 1B,illustrative embodiments of tibial inserts 100A, 100B provided inaccordance with the present disclosure are illustrated. The tibialinserts 100A, 100B may be similar in shape, with the primary differencebeing that the tibial insert 100A includes a post 108, while the tibialinsert 100B does not. As illustrated, the tibial inserts 100A, 100B areshaped for use in an orthopaedic system, which may also include afemoral component that bears on articular surfaces of the tibial inserts100A, 100B. For example, the tibial insert 100A includes a medialarticular surface 102, a lateral articular surface 104, and a centralbody 106 defined between the medial and lateral articular surfaces 102,104. The post 108 extends upwardly (i.e., superiorly) from the centralbody 106. Similarly, the tibial insert 100B includes a medial articularsurface 112, a lateral articular surface 114, and a central body 116defined between the medial and lateral articular surfaces 102, 104. Asdiscussed above, the tibial insert 100B does not include a post on thecentral body 106. The shape of the tibial inserts 100A, 100B can be anysuitable shape for orthopaedic applications. The tibial inserts 100A,100B may be formed by, for example, molding from a single material, suchas ultra-high molecular weight polyethylene (UHMWPE).

To reduce the risk of abnormal bone loading and corresponding boneabnormalities, each of the tibial inserts 100A, 100B has been modifiedso the load distribution of implants including the tibial inserts 100A,100B on surrounding bone tissue simulates natural bone loading whenimplanted. To do so, as shown, each of the inserts 100A, 100B has one ormore stiffness-modifying features 120 defined in or on the central body106, 116. In the illustrative embodiments of FIGS. 1A and 1B, thestiffness-modifying features 120 are embodied as grooves 122, 132 formedin the central body 106, 116 of the tibial inserts 100A, 100B,respectively.

For example, as shown in FIG. 1A, the tibial insert 100A includes a pairof inner walls 124 that each define a corresponding groove 122, whichillustratively extends from an anterior side 126 to a posterior side 128of the tibial insert 100A. The grooves 122 are defined in the centralbody 106 of the tibial insert 100A on either side of the post 108.Similarly, as shown in FIG. 1B, the tibial insert 100B includes a pairinner walls 134 that each define a corresponding groove 132, whichillustratively extends from an anterior side 136 to a posterior side 138of the tibial insert 100B. It should be appreciated that although eachof the tibial inserts 100A, 100B is illustrated as including two grooves122, 132, respectively, the tibial inserts 100A, 100B may includeadditional or fewer grooves in other embodiments.

The formed grooves 122, 132 reduce the stiffness of the tibial inserts100A, 100B adjacent to the grooves 122, 132, due to the lack ofsupporting material. As such, the inserts 100A, 100B are less stiff inregions around the grooves. While the stiffness-modifying features 120are illustrated as grooves in FIGS. 1A and 1B, the stiffness-modifyingfeatures 120 may be embodied as other types of modifications, as will bedescribed further herein. The depth, thickness, length, and number ofthe grooves 122, 132 can be controlled or selected such that the tibialinserts 100A, 100B display a stiffness that simulates natural boneloading after implantation. That is, the stiffness of the tibial inserts100A, 100B is reduced, relative to a typical tibial insert, such thatloading from the patient's surrounding anatomy (e.g., the femur) istransferred to the underlying tibial bone, which generally promotes bonegrowth. A location and shape of the groove(s) 122, 132 can be chosensuch that the grooves 122, 132 are formed in locations at which, forexample, the tibial insert 100A, 100B would be overly stiff due tomaterial thickness; the formed groove(s) 122, 132 can reduce thestiffness of the insert 100A, 100B in the overly stiff region byremoving material to reduce the risk of stress shielding and otherabnormal bone loading.

In the illustrative embodiments of FIGS. 1A and 1B, the groves 122, 132are embodied as straight or linear grooves (e.g., when the tibialinserts 100A, 100B are viewed in a transverse plane) that extend fromthe anterior side 126, 136 to the posterior side 128, 138 of thecorresponding tibial insert 100A, 100B. However, in other embodiments,the stiffness-modifying features 120 may be embodied as curved ornon-linear grooves, when the corresponding tibial insert is viewed in atransverse plane. For example, as shown in FIGS. 2A and 2B, tibialinserts 200A, 200B as shown and include stiffness-modifying features 120embodied as curved or non-linear grooves 222, 232 defined in the centralbody 106, 116 of the respective tibial insert 200A, 200B. For example,as shown in FIG. 2A, the tibial insert 200A includes a pair of innerwalls 224 that define corresponding curved grooves 222 in the centralbody 106 such that the curved grooves 222 curve around the post 108,which extends upwardly from the central body 106 as discussed above withregard to tibial insert 100A. Similarly, as shown in FIG. 2B, the tibialinsert 200B includes a pair of inner walls 234 that define correspondingcurved grooves 232 in the central body 116.

Similar to the grooves 122, 132, the curved grooves 222, 232 are formedand located to adjust the stiffness of the tibial inserts 200A, 200B andbone loading characteristics following implantation. Although shown inFIGS. 1A and 1B as having a general arcuate shape, it should beappreciated that the curved grooves 222, 232 may have complex curvedshapes in other embodiments to adjust the stiffness of the correspondingtibial insert 200A, 220B in particular areas.

It should be appreciated that the stiffness-modifying features 120 maybe embodied as other types of features and included in other tibialimplants and/or orthopaedic prostheses. For example, in otherembodiments, an illustrative tibial implant may include a tibial insertand a base. In some embodiments, the tibial insert comprises a polymer,such as UHMWPE, that is minimally porous and the base comprises a porousmetal, such as titanium, or a porous polymer, such as polyether etherketone (PEEK), that is at least 30-70% porous. Such a tibial insert maybe molded onto the base so the material of the tibial insert infiltratespores of the base portion to bond the two portions together.

Similar to the tibial inserts described above, the illustrative tibialinsert may include a medial articular surface, a lateral articularsurface, a central body defined between the medial and lateral articularsurfaces, and a post that extends upwardly (i.e., superiorly) from thecentral body. The illustrative tibial implant may additionally includemultiple types of stiffness-modifying features 120 formed in the tibialinsert. For example, the illustrative tibial insert may includestiffness-modifying features 120 embodied as a pair of grooves definedin the central body, which may be similar to the grooves describedabove. Each of the grooves is defined in the central body 316 onopposing sides of the post and extend from an anterior side of thetibial insert to a posterior side of the tibial insert. In theillustrative embodiment, the grooves 322 are linear when the tibialinsert is viewed in a transverse plan, but may be curved in thetransverse plane in other embodiments.

The illustrative tibial insert also includes a stiffness-modifyingfeature 120 embodied as a passageway defined in the central body.Illustratively, the passageway is embodied as a blind passageway havingan opening defined the anterior side of the tibial insert. However, inother embodiments, the passageway may be embodied as a full passagewayhaving an opening on the anterior side and an opposite opening on theposterior side. Regardless, it should be appreciated that the passagewayalso modifies the stiffness of the tibial implant by removing materialfrom a region where the tibial insert may be overly stiff. The shape,volume, and location of the passageway can be adjusted to provide theillustrative tibial implant with the desired stiffness.

In some embodiments, a therapeutic agent may be placed in one or more ofthe stiffness-modifying features 120 (e.g., in a groove and/or thepassageway). As used herein, a “therapeutic agent” is a biologicallyactive substance that may have a therapeutic effect when implanted.Exemplary therapeutic agents include, but are not limited to,anti-inflammatories, antimicrobials, cells, growth factors such as bonemorphogenetic proteins (BMP), and analgesics. The therapeutic agent maybe provided in a therapeutic agent carrier, which can act as a reservoirof the therapeutic agent. The therapeutic agent carrier may be, forexample, a sponge, gel, liquid, polymer, or other type of material thatholds the therapeutic agent therein for release, which may be immediateor gradual, into surrounding tissue after implantation. The therapeuticagent carrier may have any shape that can be placed in the slot andrelease therapeutic agent.

In another illustrative embodiment, a tibial implant may include atibial insert and a base. The illustrative tibial insert and the basemay be substantially similar to the previously-described tibial insertand base. For example, the illustrative tibial insert may include amedial articular surface, a lateral articular surface, and a centralbody defined between the medial and lateral articular surfaces, but doesnot include the previously-described post. The illustrative tibialimplant also includes multiple types of stiffness-modifying features 120formed in the tibial insert. For example, the illustrative tibialimplant includes stiffness-modifying features 120 embodied as a grooveand a passageway defined in the central body. The groove is defined in atop surface of the central body and is in fluid communication with, orotherwise connected to, the passageway. In such embodiments, the grooveand the passageway may cooperate to form tabs of the central body, whichmay be moved or pressed inwardly into the passageway via a force appliedto the central body.

In some embodiments, a therapeutic agent within a therapeutic agentcarrier may be placed in one or more of the stiffness-modifying features120 (e.g., in the groove and/or the passageway). In some embodiments,the illustrative tibial insert is configured such that high loadsexerted on the tibial implant cause compression of the therapeutic agentcarrier located in the stiffness-modifying feature 120 (e.g., thepassageway) to release the therapeutic agent into surrounding tissues.For example, compressive loads on material adjacent to the groove mayforce the tabs inwardly into the passageway to compress the therapeuticagent carrier and release therapeutic agent. Such a configuration may,for example, reduce pain and inflammation associated with large impacts.

Referring now to FIG. 3 , another illustrative embodiment of tibialinsert 300 for a tibial implant provided in accordance with the presentdisclosure is illustrated. The tibial insert 300 is illustrativelysimilar to the previously-described tibial insert. For example, thetibial insert 300 illustratively includes a medial articular surface302, a lateral articular surface 304, and a central body 306 definedbetween the medial and lateral articular surfaces 302, 304.Additionally, the tibial insert 300 includes multiple types ofstiffness-modifying features 120 formed in the central body 506,including a groove 322 and a passageway 330 defined in the central body306. The groove 322 is defined in a top surface 324 of the central body306 and is in fluid communication with, or otherwise connected to, thepassageway 330. The groove 322 and passageway 330 cooperate to form tabs340 of the central body 306, which are movable or compressible into thepassageway 330 via a suitable force applied to the central body 306.

The tibial insert 300 may also include a therapeutic agent carrierpositioned in the passageway 330 and a therapeutic agent stored in thetherapeutic agent carrier. The tibial insert 300 also includes a pair ofopenings 350 located on an anterior side 352 of the central body 306.Illustratively, the openings 350 are located on a respective side (e.g.,a medial and lateral side) of an opening 332 of the passageway 330defined on the anterior side 352 of the central body 306. Each of theopenings 350 may be sized to receive a tensioner, such as a suture. Asuture may be passed through the openings 350 and tied to force the tabs340 together. In other respects, the illustrative tibial insert 300illustrated in FIG. 3 may be substantially similar to thepreviously-described tibial inserts.

The previously described tibial inserts and components can be used toform so-called “monolithic” implants that are formed as integralimplants. In some instances, a surgeon may wish to use a so-called“modular implant,” which has a tibial insert and a tibial base that aremechanically or otherwise interlocked together but separable withoutdestroying either component.

An illustrative embodiment of a tibial base for a modular orthopaedicimplant may be formed from, for example, a metal such as cobalt chromeor titanium. The overall stiffness of the illustrative tibial base ispartially controlled by the material comprising the tibial base. Theillustrative tibial base may also comprise additional features thataffect the stiffness, including peripheral rails having a railthickness, locking features having a locking feature thickness, a cementrail having a cement rail thickness, and a shape of a keel, a stem, andone or more fins. Each of these features may be adjusted to provide thedesired stiffness of the tibial base, bearing in mind design constraintssuch as the overall geometry of the tibial base.

Another illustrative embodiment of a tibial base for a modularorthopaedic implant includes a platform configured for implantation intoa surgically-prepared tibia of a patient. The platform includes a raillocated about a periphery of the platform. The rail extends superiorlyfrom the platform and, in some embodiments, may be configured to secureor couple with a tibial insert of the modular orthopaedic implant.

The illustrative tibial base includes stiffness-modifying features 120embodied as slots or recesses formed in various locations to modify theoverall stiffness of the tibial base so the formed implant transfersloads to the bone tissue in a manner that simulates natural boneloading. For example, the illustrative tibial base includes slots orrecesses formed in the rail. Additionally, the illustrative tibial baseincludes slots or recesses formed in a top surface of the platform. Itshould be appreciated that one or more of the described slots may beshaped and sized to receive one or more therapeutic agents, which may ormay not be in a therapeutic agent carrier, to elute therapeutic agent(s)following implantation.

Another illustrative embodiment of a tibial base for a modularorthopaedic implant includes a platform configured for implantation intoa surgically-prepared tibia of a patient. The platform includes a raillocated about a periphery of the platform. The rail extends superiorlyfrom the platform and, in some embodiments, may be configured to secureor couple with a tibial insert of the modular orthopaedic implant.

The illustrative tibial base includes stiffness-modifying features 120embodied as slots or recesses formed in the rail to adjust the overallstiffness characteristics of the tibial base and formed implant. In someembodiments, one or more of the slots or recesses may be embodied as asection of the rail having a reduced height relative to other sectionsof the rail.

In yet another illustrative embodiment of a tibial base for a modularorthopaedic implant, the illustrative tibial base may be similar to thepreviously-described tibial base but include fewer slots formed in arail located on a periphery of a platform of the illustrative tibialbase such that the overall stiffness of the illustrative tibial base isgreater than the overall stiffness of the previously-described tibialbase.

It should be appreciated that similar tibial bases may differ in wherevarious slots are formed in the corresponding tibial base such that thesimilarly shaped tibial bases have different overall stiffnesscharacteristics. For example, an illustrative tibial base may include aplatform configured for implantation into a surgically-prepared tibia ofa patient. The platform includes a rail located about a periphery of theplatform. The rail extends superiorly from the platform and, in someembodiments, may be configured to secure or couple with a tibial insertof the modular orthopaedic implant. The illustrative tibial baseincludes slots or recesses formed in the rail and located so as toadjust the overall stiffness characteristics of the illustrative tibialbase and formed implant. Similarly, another tibial base may include adifferent number of slots formed in a rail located on a periphery of aplatform of the other tibial base or formed in different locations ofits rail such that the overall stiffness of the other tibial base isdifferent from the prior tibial base.

Referring now to FIGS. 4A-4C, another illustrative embodiment of atibial base 400 for a modular orthopaedic implant provided according tothe present disclosure is shown in FIGS. 4A and 4B, with a known tibialbase 410 shown in FIG. 4C for comparison. Each of the tibial bases 400,410 include a fin or keel 450 that extends inferiorly from a bottomsurface 402, 412 of the tibial base 400, 402. The tibial base 400,unlike the tibial base 410, has a stiffness-modifying feature 120 in theform of slots or undercuts 452 formed in the fin 450. The slots 452 inthe fin 450 can reduce the stiffness behavior of the tibial base 400,and thus the stiffness behavior of an implant incorporating the tibialbase 400. The size, location, and number of slots formed in the fins 450can be adjusted to adjust the overall stiffness characteristics of thetibial base 400.

It should be appreciated that the previously described tibial bases withstiffness-modifying features can be coupled with tibial inserts thatalso include stiffness-modifying features in order to control theoverall stiffness characteristics of a formed implant. Therefore, theoverall stiffness characteristics of implants provided according to thepresent disclosure can be adjusted in many different ways. Illustrativeways of adjusting the overall stiffness characteristics of a tibial baseand/or tibial insert, or a monolithic implant, include but are notlimited to: selection of metal material and/or treatment for one or moreof the components; selection of polymer material and/or treatment forone or more of the components; additive manufacturing to add varyingdegrees of flexibility in the metal and/or polymer material(s); andintroducing slots or other openings with varying locations,orientations, depths, and widths. By adjusting the overall stiffnesscharacteristics of implants to more closely simulate normal bone tissueloading, the risk of abnormal bone growth can be reduced.

Another embodiment of a tibial base may comprise a polymer, such asUHMWPE or PEEK, and have porous metal pads affixed to a bottom surfaceof the illustrative tibial base. For example, the illustrative tibialbase may include multiple (e.g., four) separate porous metal padsattached to the bottom surface that each have a corresponding post. Insome embodiments, the illustrative tibial base may include a keelextending inferiorly from the bottom surface. The keel may include aslot that extends superiorly, which splits the keel into two sections(e.g., medial and lateral sections). The slot may further adjust thestiffness of the tibial. Conversely, in another illustrative tibialbase, the keel may be solid and not include a slot formed therein.Additionally, the other illustrative tibial base may include a singleporous pad attached to the bottom surface. As such, described tibialbases may have different stiffness due to the inclusion of differentstiffness-modifying features.

Referring now to FIG. 5 , another illustrative embodiment of a tibialbase 500 provided according to the present disclosure is illustrated.The tibial base 500 may be formed from a polymer, such as UHMWPE orPEEK. The tibial base includes a polymer platform 502 having a superioror top surface 504 and an inferior or bottom surface 506 opposite thesuperior surface 504, which is configured to rest on a resected tibiaafter implantation. Additionally, the tibial base 500 may include a keel550 extending inferiorly from the inferior surface 506 of the polymerplatform 502. To modify the stiffness of the tibial base 500, theinferior surface 506 may have several stiffness-modifying features 120formed therein. For example, as illustrative shown in FIG. 5 , thestiffness-modifying features 120 may be embodied as a one or moregrooves, slots, or openings 510 defined in the inferior surface 506 ofthe tibial base 500. The illustrative slots 510 are defined in theinferior surface 506 in an anterior-posterior direction, but may bedefined in the inferior surface 506 in other directions in otherembodiments. Thus, it should be appreciated that the inferior surface506 of the tibial base 500 provided according to the present disclosurecan also be modified to modify the overall stiffness characteristics ofthe base portion and the formed implant.

Referring now to FIG. 6 , another illustrative embodiment of a tibialbase 600 provided according to the present disclosure is illustrated.The tibial base 600 may be formed from a polymer, such as UHMWPE orPEEK. The tibial base 600 includes a polymer platform 602 having asuperior or top surface 604 and an inferior or bottom surface 606opposite the superior surface 604, which is configured to rest on aresected tibia after implantation. Additionally, the tibial base 600 mayinclude a keel 650 extending inferiorly from the inferior surface 606 ofthe polymer platform 602.

The inferior surface 606 is illustratively at least partially covered bya porous ingrowth surface. The porous ingrowth surface may comprise, forexample, a porous metal, such as titanium, or polymer, such as PEEK,that has a porous structure to encourage tissue ingrowth into thematerial to fixate the tibial base 600 to the implantation site. In someembodiments, the porous ingrowth surface has stiffness-modifyingfeatures 120, such as slots or grooves 610, formed in the porousmaterial to modify the stiffness of the porous ingrowth surface, andthus the overall stiffness characteristics of the formed implant.Illustratively, the slots 610 are defined in the porous ingrowth surfacesuch that the slots 610 intersect each other to form a “mesh” of slots.Thus, it should be appreciated that the inferior surface 606 of baseportions provided according to the present disclosure can have porousingrowth surfaces with stiffness-modifying features to modify theoverall stiffness characteristics of the base portion and the formedimplant.

While the disclosure has been illustrated and described in detail in thedrawings and foregoing description, such an illustration and descriptionis to be considered as exemplary and not restrictive in character, itbeing understood that only illustrative embodiments have been shown anddescribed and that all changes and modifications that come within thespirit of the disclosure are desired to be protected.

There are a plurality of advantages of the present disclosure arisingfrom the various features of the method, apparatus, and system describedherein. It will be noted that alternative embodiments of the method,apparatus, and system of the present disclosure may not include all ofthe features described yet still benefit from at least some of theadvantages of such features. Those of ordinary skill in the art mayreadily devise their own implementations of the method, apparatus, andsystem that incorporate one or more of the features of the presentinvention and fall within the spirit and scope of the present disclosureas defined by the appended claims.

1. A tibial insert comprising: a medial articular surface; a lateralarticular surface; a central body formed between the medial articularsurface and the lateral articular surface; an inner wall defining (i) apassageway extending into the central body and (ii) a groove defined ona top surface of the central body, wherein the groove is in fluidcommunication with the passageway; and a therapeutic agent disposed inthe passageway.
 2. The tibial insert of claim 1, wherein the passagewayis a blind passageway having an opening on an anterior side of thecentral body or a posterior side of the central body.
 3. The tibialinsert of claim 1, wherein the passageway extends through the centralbody and includes a first opening on an anterior side of the centralbody and a second opening on a posterior side of the central body. 4.The tibial insert of claim 1, wherein the grove extends from theanterior side of the tibial insert to the posterior side of the tibialinsert
 5. The tibial insert of claim 1, wherein the groove defines apair of tabs of the central body that are movable into the passageway inresponse to a force applied to the tabs, and wherein the tabs cause arelease of the therapeutic agent from the passageway in response tobeing moved into the passageway.
 6. The tibial insert of claim 5,further comprising a pair of openings defined on an anterior side of thecentral body, each of the openings being configured to receive atensioner operable to move the tabs of the central body to cause therelease of the therapeutic agent from the passageway.
 7. A tibial insertcomprising: a medial articular surface; a lateral articular surface; anda central body formed between the medial articular surface and thelateral articular surface, wherein the central body includes anelongated groove defined therein.
 8. The tibial insert of claim 7,wherein the elongated groove is linear when the tibial insert is viewedin a transverse plane.
 9. The tibial insert of claim 7, wherein theelongated groove is a curved when the tibial insert is viewed in atransverse plane.
 10. The tibial insert of claim 7, wherein theelongated groove extends from an anterior side of the central body ofthe tibial insert to a posterior side of the central body of the tibialinsert.
 11. The tibial insert of claim 7, wherein the elongated grooveextends linearly from an anterior side of the central body of the tibialinsert to a posterior side of the central body of the tibial insert. 12.The tibial insert of claim 7, wherein the elongated groove curves froman anterior side of the central body of the tibial insert to a posteriorside of the central body of the tibial insert.
 13. The tibial insert ofclaim 7, further comprises a post extending superiorly from the centralbody, wherein the elongated groove comprises a first elongated groovedefined in the central body medially of the post, and wherein the tibialinsert further includes a second elongated grove defined in the centralbody laterally of the post.
 14. The tibial insert of claim 13, whereinat least one of the elongated grooves is linear when the tibial insertis viewed in a transverse plane.
 15. The tibial insert of claim 13,wherein at least one of the grooves is curved when the tibial insert isviewed in a transverse plane.
 16. A tibial prosthesis for implantationinto a surgically-prepared tibia of a patient, the tibial prosthesiscomprising: a polymer platform having a superior surface and an inferiorsurface opposite the superior surface; and a keel extending from theinferior surface of the polymer platform, wherein the polymer platformincludes a plurality of stiffness-modifying features defined in theinferior surface.
 17. The tibial prosthesis of claim 16, wherein theplurality of stiffness-modifying features includes a plurality of slotsdefined in the inferior surface of the polymer platform.
 18. The tibialprosthesis of claim 17, wherein each slot of the plurality of slots isdefined in the inferior surface of the polymer platform in ananterior-posterior direction.
 19. The tibial prosthesis of claim 17,wherein the inferior surface of the polymer platform comprises a porousingrowth surface and at least two slots of the plurality of slotsintersect each other.